1. Field of the Invention
The present invention relates to a cryptographic communication method, a file access system and a recording medium.
Along with the widespread use of personal computers, a communication using a computer network such as an electronic mail has become an essential tool for business. Considering that data are not only used in an individual computer but also transmitted via a network, the data security should be realized totally.
2. Description of the Prior Art
Conventionally, a communication method is known well in which a key is used for enciphering data to be transmitted for data security in the electronic mail, and the same key is used in the reception side for decoding received data.
The applicant has proposed a file access system for security of files used in a personal computer as disclosed in Japanese unexamined patent publication No. 10-301856. According to this method, while the key is activated after the user is authenticated, any file is automatically enciphered by entering the file in a designated folder. When reading the file in the folder, the file is automatically decoded. A user who has the right can read and can edit the enciphered file in the same way as a normal file without considering that the file is enciphered.
The above-mentioned file access system is an outstanding system for dealing with various contents such as a database or a file within a personal computer.
However, the system is not suitable for transmitting the contents to another computer after enciphering them, or for using enciphered contents that were transmitted from another computer after enciphering by a personal key.
For example, when transmitting enciphered contents as an attached file of an electronic mail, the attached file is automatically decoded by the read command for making the attached file. In order to prevent this situation from being generated, it is necessary to stop the function of the key in advance. However, this operation is so complicated that there is a possibility of transmitting the attached file without enciphering.
In addition, when transmitting non-enciphered contents as an enciphered attached file, the key should be activated for the enciphering, and then the function of the key should be stopped before making the attached file by the read command. This operation is also complicated, and there is a possibility of transmitting an attached file that is decoded by a misoperation.